We found in our previous studies that the in vivo line tumor YAC induces suppressor cells in A mice while the in vitro, subline of this tumor induces memory cells. Spleen cells from YAC-1 injected mice can generate anti-YAC cytotoxic response (when sensitizer is absent) and anti YAC-1 cytotoxic response (when sensitizer YAC-1 is present in the culture). Addition of splenocytes from YAC injected mice into the cultures abrogates the cytotoxic responses. The aim of this proposal is to characterize both the suppressor and the memory cells, to determine the mechanism of suppression on memory induction and to apply the findings to the immunotherapy model. The nature of both suppressor and memory cells will be determined by using reagents and procedures which isolate or characterize T cells, B cells, K cells or macrophages. The physical properties of both memory and suppressor cells will be determined by exposing them to irradiation and freezing-thawing conditions. The mechanism of suppression and memory induction will be studied by determining the specificity of both suppressor and memory cells, using immunoabsorbent monolayers. We shall also focus our attention on the mode of communication between suppressor and memory cells. In addition, we shall determine the target cells of the suppression. In a different set of experiments, we shall determine the reversibility of YAC-1 subsequent to its inoclation back into A mice. Finally, we shall determine the possibility of shifting in vivo immunological balance to favor antitumor immunological rejection over suppression. YAC tumor-bearing A mice will undergo adult typmectomy (to remove selectively suppressor cells) and will be YAC-1 immunized (to induce memory cells). The ability of such mice to reject tumor will be determined.